The present invention refers, in general, to a reciprocating compressor to be applied to refrigeration systems and having one or two pistons reciprocating inside a cylinder and driven by a linear motor. More specifically, the invention refers to a coupling provided between each piston and a resonant system associated therewith.
In a reciprocating compressor driven by a linear motor and provided with one or two pistons, the gas suction and compression operations are achieved by the reciprocating axial movements of each piston inside a cylinder mounted within a hermetic shell, each piston being driven by a respective actuating means, which carries magnetic components operatively associated with the linear motor affixed to the hermetic shell of the compressor.
As known from the prior art, each piston-actuating means assembly is necessarily connected to a resonant spring affixed to the hermetic shell of the compressor, in order to operate as a guide for the axial displacement of the piston and to make the whole system act resonantly in a pre-established frequency, allowing the linear motor to be adequately dimensioned, in order to continuously supply energy to the compressor under operation.
Since the manufacturing tolerances of the resonant springs are normally much higher than the project gap provided between the piston and the cylinder, there is a need for providing a coupling between the piston-actuating means assembly and the resonant spring, in order to absorb alignment deviations between said components, so as to prevent the piston from suffering radial loads and/or bending moments and forces which may induce it to work in an inclined position when axially moving inside the cylinder, increasing the attrition with the cylinder wall and causing wear.
The resonant spring does not have a manufacturing dimensional precision to assure the piston to be perfectly centered during its reciprocating operational displacement inside the cylinder, without being submitted to radial efforts during the elastic deformations of the resonant spring in opposite axial directions during the suction and compression strokes of the piston.
In a known prior art solution, the coupling provided between the actuating means and the resonant spring is in the form of a long rod, axially arranged and having a certain previously established flexibility obtained by reducing the thickness of the rod, which results in a better absorption of alignment deviations. However, even making the rod very thin, it is not possible to completely eliminate the radial rigidity, since it is usually impossible to increase the length of the rod to a value sufficient to make irrelevant the radial efforts transmitted by said rod to the piston. Thus, radial force components will always be present, acting on the piston. On the other hand, using a thin rod may cause bending deformations in said rod during the time in which more intense axial forces are being applied thereon, that is, at the end of the suction stroke and at the beginning of the compression stroke, also causing problems of undue attrition between the piston and the cylinder.
In short, it may be said that the known solutions to provide the coupling between the piston and the resonant spring of a reciprocating compressor with a linear motor have not been sufficiently effective to absorb the angular and radial disalignments between the piston and spring axes and thus eliminate, in an economically viable way, the undue radial efforts which said coupling transfers to the piston as a function of the disalignments mentioned above.
Besides the problem related to the absorption of efforts mentioned above, the known coupling makes very difficult, when not impracticable, the tight fluid connection between a suction valve and/or a discharge valve mounted on the upper face of the piston, and a respective inlet tube provided through the wall of the hermetic shell. In this type of assembly for the suction and/or discharge valves, the connection of the valve with the outside of the hermetic shell is axially achieved through the inside of the piston body and by means of a flexible tubular connection, connecting the piston to the inlet tube provided in the wall of the hermetic-shell.
In the known constructions, the coupling does not allow, unless through very complex constructive arrangements, the tight fluid communication between the inside of the piston and a respective inlet tube provided in the wall of the hermetic shell and coupled to a refrigeration system.
Thus, it is an object of the present invention to provide a reciprocating compressor driven by a linear motor and having a coupling between the piston and the resonant spring, with a compact construction and which may absorb radial and angular disalignments between the piston and the spring axes, avoiding that said disalignments result in the application of radial efforts on the piston during the operation of the compressor.
It is also an object of the present invention to provide a coupling as mentioned above, which allows to establish, by means of a simple constructive arrangement, a tight fluid communication between the inside of the piston and the outside of the hermetic shell.
These and other objectives are achieved by a reciprocating compressor driven by a linear motor, comprising: a hermetic shell; a linear motor and a cylinder affixed inside the hermetic shell; at least a piston reciprocating inside the cylinder and axially affixed to an end of a rod; an actuating means coupling the piston to the linear motor; and a resonant spring transversally affixed inside the hermetic shell and axially coupled to the rod.
According to the invention, each of the parts defined by the rod and by the resonant spring has two contact surfaces lying on orthogonal planes in relation to the cylinder axis and axially spaced from each other, each of said surfaces facing a respective confronting contact surface of the other part, between each pair of confronting contact surfaces being provided a spacing body, which is loosely and coaxially mounted around the rod and has two axially opposite contact surfaces lying on orthogonal planes in relation to the cylinder axis, each of said contact surfaces being forced to seat against one of said confronting contact surfaces by means of a pair of convex surface portions, which are symmetrical and opposite in relation to the cylinder axis, each pair of convex surface portions being operatively associated with the same spacing body, with the convex surface portions thereof defining an orthogonal alignment in relation to the other pair and to the cylinder axis.